What Is a Transfer Switch Interlock?
Transfer Switch Interlock is a mechanical or listed electrical device that coordinates a generator connection with a building’s utility supply. The interlock permits the generator source to feed selected circuits only when the utility source is disconnected. Its main purpose is to prevent both power sources from being connected to the panel at the same time.
Quick Facts About Transfer Switch Interlock
Category
Generator source-control device
Used for
Managing utility and generator connections
Common confusion
It is not an automatic transfer switch
Also called
Generator Interlock Kit, Generator interlock
Often discussed with
Generator Transfer Switch Installation
Key Takeaways About Transfer Switch Interlock
- It uses physical source selection at the electrical panel.
- It supports generator power for selected building circuits.
- It is not the same as an automatic transfer switch.
How Transfer Switch Interlock Works
A Transfer Switch Interlock uses a sliding plate, blocking mechanism, or related assembly at the electrical panel. The mechanism allows the utility main breaker or generator breaker to occupy the permitted position, while physically blocking the other source. Source selection happens at the panel, so the arrangement must match the panel design and the generator connection.
Related glossary terms: Automatic Transfer Switch, Generator Inlet, Load Calculation.
During generator operation, the utility source is opened before the generator source is closed. Selected branch circuits then receive power through the panel from the connected source. A generator inlet provides the connection point for a portable generator, while the interlock manages which source can energize the panel. An automatic transfer switch performs source changes through control equipment without requiring manual breaker operation.
From the Earth Electric team
When we inspect a transfer switch interlock, we check the panel type, breaker arrangement, generator connection, and physical movement of the interlock. We also verify that the selected circuits match the intended generator setup. Our team treats the interlock as part of the complete transfer arrangement, not as an isolated panel accessory.
Transfer Switch Interlock in Practice: A Real-World Example
A Miami home has a portable generator connected through a generator inlet to selected panel circuits. The transfer switch interlock blocks the generator breaker until the utility main is open, then permits generator power to reach those circuits.
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Related Terms
Automatic Transfer Switch
An Automatic Transfer Switch is an electrical switching device that moves a connected load from normal…
Generator Inlet
A generator inlet is a permanently installed connection point that receives power from a portable generator…
Load Calculation
Load Calculation is an engineering assessment that estimates the electrical demand a property places on its…
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